1. Field
One embodiment of the invention relates to a technology for increasing resolution of an image.
2. Description of the Related Art
Frame rate conversion is a technology for increasing a frame rate representing the number of frames of an input video signal per second to thereby display a smooth image of a moving object. A conventional technology of such frame rate conversion is disclosed in, for example, Japanese Patent Application Publication (KOKAI) No. 2007-82030. According to the conventional technology, motion compensation is performed on each of a plurality of image data sets that constitute video data to calculate a motion vector between two frames adjacent in time. An interpolation frame is generated based on the motion vector to be interpolated between the two frames.
Meanwhile, with the widespread of high-resolution televisions and displays, the resolution of image data becomes higher. As the resolution of an image signal increases, the data volume involved in image processing on the image signal increases. Therefore, there is a need for a technology capable of more efficient image processing. Accordingly, there has been proposed the technology of image processing referred to as super resolution processing (super-resolution enhancement). In the super resolution processing, an original pixel value is estimated from a low-resolution image signal, and the pixels are increased to obtain a high-resolution image signal. Thus, the super resolution processing increases the resolution of an image signal while maintaining the sharpness thereof. Reference may be had to, for example, Japanese Patent Application Publication (KOKAI) Nos. 2007-336239 and 2007-310837.
To display more sharp and smooth image, an input image signal needs not only to be interpolated with interpolation frames to change the frame rate but also to be subjected to the super-resolution enhancement.
Suppose that the super resolution processing is performed after the frame rate conversion of a video signal. With the conventional technology of frame rate conversion, a motion compensation error may occur due to erroneous estimation of a motion vector in motion compensation for generating an interpolation frame. If the super resolution processing is performed on image data having a motion compensation error, the motion compensation error is emphasized due to the super resolution processing. As a result, the super resolution processing has an adverse effect on an image displayed on a television or a display and degrades the image quality.
Beside, interpolation frames generated and interpolated between frames of input image data increase the original number of the frames of the image data. If the super resolution processing is performed after the interpolation frames are interpolated between the frames, the super resolution processing is required to be performed on the interpolation frames as well as the frames of the image data. This increases the amount of the super resolution processing.
If the super resolution processing is performed on the frames of moving image data except for interpolation frames, it means that the super resolution processing is not performed on all the frames of the moving image data. Thus, this reduces the effect of improving the sharpness of the moving image.